This invention relates in general to the production of linear stock material such as tube stock material and round bar stock material, and more particularly to an machine vision method and apparatus for the automated determination of the straightness of linear stock material during production.
Ideally, tube stock and round bar stock materials, generally referred to herein as linear stock material, should emerge from the mills in which they are produced in a perfectly straight configuration for the entire production length. But typically some deviation from perfectly straight exists in the linear stock material, which is acceptable for most purposes so long as the deviation is within prescribed tolerances. Currently mill operators conduct visual inspections to determine if sections of the linear stock material being produced by a mill falls within the prescribed tolerances. But this leaves much of the produced material without a quantitative inspection, and fails to detect deviation trends that could be corrected by making adjustment in the operation of the mill.
The typical inspection of a length of linear stock material, which may be between 4.5 meters to 12.0 meters in length, involves removing it from the mill in which it is produced and placing it on a flat table or level rails. There, an inspector using the flat surface of the table, determines the direction of any bow present in the linear stock material, and on which side of the bow is most pronounced—that is to say, the inspector determines the angular orientation, about the circumference of the linear stock material, the bow creates the greatest concavity.
Having located the side with the greatest concavity, the inspector places a precision straight edge, which can be typically one meter in length, against that side of the linear stock material. Any deviation from straight appears as a gap between the surface of the linear stock material and the straight edge, and is usually measured with a feeler gauge between the ends of the precision straight edge. The procedure is repeated for several segments along the length of the tube stock. Tube stock material and round bar stock material undergo similar inspection procedures for determining the presence of any deviation from an ideal straightness.
If quantitative inspection results are required, the typical inspecting procedure consumes a considerable amount of time, and without incurring inordinate expense, cannot be performed on all points of the material from a full production run at a mill. Thus, quantitative inspections are performed only on linear stock material selected using a screening method from a production run of a mill.